Reduction of the nonspecific animal toxicity of anti-Tac(Fv)-PE38 by mutations in the framework regions of the Fv which lower the isoelectric point.

Abstract

Anti-Tac(Fv)-PE38, also called LMB-2, is a very active recombinant immunotoxin that has produced eight responses, including a durable clinical complete remission in a recently completed phase I trial of leukemias and lymphomas. Dose escalation was limited by liver toxicity. We have noted that the Fv of anti-Tac has an isoelectric point (pI) of 10.2. We hypothesize that the overall positive charge on the Fv portion of anti-Tac(Fv)-PE38 contributes to nonspecific binding to liver cells and results in dose-limiting liver toxicity. We have used a mouse model to investigate the basis of this toxicity and found that lowering the pI of the Fv of anti-Tac from 10.2 to 6. 82 by selective mutation of surface residues causes a 3-fold decrease in animal toxicity and hepatic necrosis. This change in pI did not significantly alter the CD25 binding affinity, the cytotoxic activity toward target cells, or antitumor activity, resulting in a 3-fold improvement in the therapeutic index. If this decreased toxicity occurs in humans, it should greatly increase the clinical utility of this immunotoxin.

• Authors: M Onda, R J Kreitman, G Vasmatzis, B Lee, I Pastan
• Journal: Journal of immunology (Baltimore, Md. : 1950) (J Immunol) Vol. 163 Issue 11 Pg. 6072-7 (Dec 01 1999) ISSN: 0022-1767 [Print] United States
• PMID: 10570296 (Publication Type: Journal Article)

Chemical References

• Antibodies, Monoclonal
• Antibodies, Neoplasm
• Antineoplastic Agents
• B3(Fv)-PE38KDEL recombinant immunotoxin
• Bacterial Toxins
• Exotoxins
• Immunoglobulin Fragments
• Immunotoxins
• Recombinant Proteins
• Virulence Factors
• immunoglobulin Fv
• ADP Ribose Transferases
• Pseudomonas aeruginosa exotoxin A

Topics

• ADP Ribose Transferases
• Animals
• Antibodies, Monoclonal
• Antibodies, Neoplasm (genetics, toxicity)
• Antineoplastic Agents (toxicity)
• Bacterial Toxins
• Dose-Response Relationship, Drug
• Exotoxins (genetics, toxicity)
• Female
• Immunoglobulin Fragments (genetics, toxicity)
• Immunotoxins (genetics, toxicity)
• Isoelectric Point
• Liver (drug effects)
• Mice
• Mice, Nude
• Mutation
• Neoplasms, Experimental (drug therapy)
• Recombinant Proteins (toxicity)
• Structure-Activity Relationship
• Toxicity Tests
• Virulence Factors